1 Reply Latest reply on Feb 24, 2010 11:19 AM by 1-E9V5A2

    Frequency analysis results

      Hi,

      i have done a frequency analysis on one of the machine base and obtained my list of resonant frequency. On the machine base placed is cross slide and the saddle. If I have to find out the behaviour of my machine base, I should check the motor driving the cutting tool its frequency and the natural frequency of machine base should not coincide am i right in my approach. If it coincides I will have to make design changes so that i take natural frequency of machine base away from that of motor frequency. Please correct me if I am wrong thanks

        • Re: Frequency analysis results

          Shankar,

           

          I believe you're understanding it rightly.  If, for example, your motor runs at 1500rpm, you can convert that to Hz.  60rpm = 1Hz.  So your motor is running at 25Hz.  If there was any imbalance in your motor (e.g. a shaft isn't quite perfectly round) it will probably put a small force on your weldment 25 times every second.  In other words, there would be a vibration input at 25Hz.

           

          So if your weldment has a natural frequency of 25Hz, it will want to dance right along with the motor's input vibration.  Eventually, the vibations displacement will add up and add up and you'll have catastrophic failure of your weldment.  So you want your frame weldment to have a natural frequency about 2 times above 25Hz (in this example) so that when the motor is running at its fastest, it won't wreck the frame.

           

          If your machine base's natural frequency is less than that of the motor, that means that while the motor is getting up to speed, it will pass through the resonance range of your machine base, causing a lot of excessive vibration. Some machines have this problem and there's nothing to be done about it but have a strategy to pass through the resonance zone in the safest possible way. You'd want to avoid this if you can.

           

          David